Release pattern for potassium from decomposing forest needle and leaf litter. Long-term decomposition in a Scots pine forest .9.

A general pattern for the dynamics of K in decomposing leaf and needle litters is described, based on 139 litter decomposition studies carried out in forests of northern and central Europe and the northern United States. We distinguished an initial phase of fast changes in K concentration and a later one in which the litter was close to humus and all K appeared to be immobile. In the initial phase the rate of change in K concentration was related to the initial K concentration: the higher the initial concentration, the faster its decrease and the faster the quantitative release of K. For litters with particularly low initial K concentrations, an increase in concentration was observed from the very start of decomposition. In the late phase a slight increase in concentrations was observed. After ca. 60% accumulated mass loss, K concentrations approached similar levels in various litter types, irrespective of the litter type and initial concentrations. We also estimated a theoretical equilibrium state at which no change in K concentration should be expected. According to our estimates these equilibrium concentrations ranged from approx. 0.8 mg/g dry mass of litter for Scots pine to approx. 1.2 mg/g dry mass for deciduous litter types. The estimate of K concentration in Scots pine litter in late decomposition stages was very close to that measured in the humus at the same site. Based on the wide variety of litter types and sites studied we conclude that the pattern suggested for K dynamics in decomposing litter holds at least for European coniferous forests north of the Alps and the Carpathians.